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fix: replace busy-wait loop in BallThread with wait/notify (#2977) #3614

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fix: replace busy-wait loop in BallThread with wait/notify (#2977) #3614

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70d5788
fix: replace busy-wait in BallThread with wait/notify (#2977)
KANISHKMAKKAR Sep 29, 2026
7c10fec
docs: update twin README to match BallThread fix
KANISHKMAKKAR Sep 29, 2026
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33 changes: 24 additions & 9 deletions twin/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -88,36 +88,51 @@ public class BallItem extends GameItem {
public class BallThread extends Thread {
@Setter
private BallItem twin;
private final Object lock = new Object();
private volatile boolean isSuspended;
private volatile boolean isRunning = true;

public void run() {
while (isRunning) {
if (!isSuspended) {
twin.draw();
twin.move();
}
try {
Thread.sleep(250);
synchronized (lock) {
// Wait to be notified instead of polling, so resuming takes effect immediately.
while (isSuspended && isRunning) {
lock.wait();
}
}
if (isRunning) {
twin.draw();
twin.move();
Thread.sleep(250);
}
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
}

public void suspendMe() {
isSuspended = true;
synchronized (lock) {
isSuspended = true;
}
LOGGER.info("Begin to suspend BallThread");
}

public void resumeMe() {
isSuspended = false;
synchronized (lock) {
isSuspended = false;
lock.notifyAll();
}
LOGGER.info("Begin to resume BallThread");
}

public void stopMe() {
this.isRunning = false;
this.isSuspended = true;
synchronized (lock) {
this.isRunning = false;
this.isSuspended = true;
lock.notifyAll();
}
}
}
```
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34 changes: 25 additions & 9 deletions twin/src/main/java/com/iluwatar/twin/BallThread.java
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,8 @@ public class BallThread extends Thread {

@Setter private BallItem twin;

private final Object lock = new Object();

private volatile boolean isSuspended;

private volatile boolean isRunning = true;
Expand All @@ -44,30 +46,44 @@ public class BallThread extends Thread {
public void run() {

while (isRunning) {
if (!isSuspended) {
twin.draw();
twin.move();
}
try {
Thread.sleep(250);
synchronized (lock) {
// Wait to be notified instead of polling, so resuming takes effect immediately.
while (isSuspended && isRunning) {
lock.wait();
}
}
if (isRunning) {
twin.draw();
twin.move();
Thread.sleep(250);
}
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
}

public void suspendMe() {
isSuspended = true;
synchronized (lock) {
isSuspended = true;
}
LOGGER.info("Begin to suspend BallThread");
}

public void resumeMe() {
isSuspended = false;
synchronized (lock) {
isSuspended = false;
lock.notifyAll();
}
LOGGER.info("Begin to resume BallThread");
}

public void stopMe() {
this.isRunning = false;
this.isSuspended = true;
synchronized (lock) {
this.isRunning = false;
this.isSuspended = true;
lock.notifyAll();
}
}
}
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